1. Field of the Invention
The present invention relates to a method for analyzing anaesthetic agents, suitable for identifying anaesthetic agents.
The present invention also relates to an analyzer for analyzing anaesthetic agents, suitable for identifying anaesthetic agents.
2. Description of the Prior Art
Anaesthetic agents are used for inducing anaesthesia and are administered to a patient in gaseous form. The anaesthetic agent is generally present in liquid form in a vaporizer and is vaporized into gaseous form therein. There are numerous anaesthetic agents. Desflurane, enflurane, halothane, isoflurane and sevoflurane are the most commonly used ones today. These agents are administered in different concentrations, and it is important that only one of them is administered at a time to a patient. Erroneous concentrations or a mixture of different anaesthetic agents could pose a risk to the patient. At worst, the patient could be seriously injured or even die. Liquid anaesthetics must also be handled with great care, since inhaling them at high concentrations is hazardous. Even long-term exposure to low concentrations of anaesthetic can pose risks to health. This is primarily a problem for hospital personnel.
Maintaining the most reliable conditions possible in the use of anaesthetic machines therefore is of the utmost importance.
Patients respond differently, however, to the aforementioned anaesthetic agents. One anaesthetic might evoke an allergic response in some patients, making it necessary to switch to another anaesthetic quickly.
One anaesthetic agent may be more suitable for use during the induction phase of anaesthesia but not during the remaining narcosis. One such anaesthetic agent is halothane, often used to anaesthetize children, since inspiring vaporized halothane is not unpleasant, but the agent could cause e.g. liver damage.
Most anaesthetic machines are therefore devised to enable the anaesthetist to switch to different anaesthetic agents relatively simply with no risk of simultaneously delivery of two different anaesthetic agents at the same time.
Different safety systems are also available. For example, special keyed connectors between respective gas bottles and vaporizers and/or color-coding when liquid anaesthetic in the vaporizer is replenished are used to prevent a mixture of anaesthetic agents in the vaporizer.
A disadvantage of these types of safety system is that they do not preclude human error. Residual anaesthetic in a vaporizer could, after use, be emptied by mistake into a container holding some other anaesthetic agent or be erroneously marked. Mixing would then occur the next time that an erroneously marked liquid is poured into a vaporizer.
The risk of this happening is greater than most people would believe. Anaesthetics are expensive, and many hospitals cannot afford to just throw away superfluous anaesthetic. Not all vaporizers are equipped with proper receivers for the keyed connectors. In these cases the keyed connector on the bottle is removed for filling the vaporizer.
Identification of the anaesthetic in a vaporizer and/or anaesthetic machine therefore provides for more reliable protection of the patient. Delivery can be stopped immediately if an erroneous anaesthetic agent is identified in the system.
Anaesthetic agents can be optically identified with absorption spectrophotometry from their respective refractive index, density, absorption in other materials, dielectric constant, etc.
A major problem encountered in anaesthetic identification is the similar chemical structures of different anaesthetic agents, resulting in similar properties. Several of the aforementioned methods usually require the use of highly specialized analysis equipment, or e.g. the concentration of the anaesthetic agent must be known. A number of these methods are also incapable of sensing mixtures of different anaesthetic agents. It is further not always possible, with the known methods, to detect contamination of or chemical changes in an anaesthetic agent.
Finding alternative methods and analyzers for analyzing and identifying anaesthetic agents in a simple, reliable and exclusive manner therefore is desirable, preferably with the ability to identify mixtures of different anaesthetic agents, contamination of anaesthetic agents and even chemical changes in an anaesthetic agent.
An object of the present invention is to provide a method for fast, simple and reliable analysis of anaesthetic agents, primarily for anaesthetic agents identification and for determination of changes in anaesthetic agents, especially mixing of different agents, contamination of an agent and chemical changes in an agent.
The above object is achieved in accordance with the principles of the present invention in a method for analyzing anaesthetic agents wherein at least one parameter that is directly related to dielectric polarization in an anaesthetic agent is determined, and the anaesthetic agent is analyzed (as to, for example, identity, mixture with other anaesthetic agents, contamination, etc.) dependent on the measured parameter directly related to dielectric polarization.
Dielectric polarization is a property of different materials caused by the polarization of molecules and atoms subjected to an electrical field. This polarization takes a certain amount of time and dissipates when the electrical field is removed. Thus, polarization reflects properties on the molecular and atomic level and is also completely independent of the dielectric constant. Since the effect depends on the movement of molecules and atoms, it is most pronounced in liquid and gaseous substances.
Measurements made of anaesthetic agents in liquid form have shown that they differ in their dielectric polarization. Anaesthetic agents therefore can be identified from their dielectric polarization or a parameter directly related to it. The differences are also sufficiently distinct for practical use.
Changes caused by fouling, mixing with other agents, chemical action and other factors, leading to a quantifiable change in the anaesthetic agent""s dielectric polarization properties, can be determined with the method.
One advantageous way of identifying such a parameter is to sequentially expose the anaesthetic agent to different electrical fields. This creates a potential difference across the anaesthetic agent. A high-impedance voltmeter can then be used to measure the voltage component developing across the anaesthetic agent due to residual polarization. The voltage component is determined in relation to the created potential difference.
One way to create the potential difference is to short-circuit the electrical field during a time period.
The voltage/potential applied across the anaesthetic agent should be less than the electrochemical potential for the anaesthetic agent or components therein.
This determination can be made with greater precision if several measurements are performed with differing durations for the exposure to the electrical field.
Another way to increase identification precision, particularly when a large number of substances are to be identified, is to carry out determination of the parameter at different frequencies. A pattern xe2x80x9cfingerprintxe2x80x9d or spectrum then can be obtained for each anaesthetic agent, thereby increasing identification specificity. Pattern identification can be performed in a pattern recognition system or an artificial neural network and is iteratively taught to recognize pure anaesthetic agents and non-pure anaesthetic agents (contaminated agents, mixtures of different agents or chemically changed agents).
Other specific advantages are also achieved. When liquid anaesthetic in the vaporizer is identified, a relatively simple concentration meter of the known type can be arranged to measure the concentration of the anaesthetic agent in gaseous form. The simple concentration meter obtains information as to the identity of the anaesthetic agent, and appropriate scaling of the sensor signal from the concentration meter can then be performed.
Dielectric polarization can be determined in a number of ways in order to increase the specificity of qualitative analysis even further. A combination of different measurement methods can then result in a refined gradation of differences that cannot be achieved with a single measurement method.
Alternatively, a number of different parameters directly related to dielectric polarization can be determined and utilized in the same way.
The method can also be supplemented with determination of another property of the anaesthetic agent, e.g. molecular weight, absorption spectra etc. Merging different properties can then further increase specificity. This applies in particular to specify more precisely the degree of contamination, mixing, etc.
The above object is achieved in an analyzer according to the invention having a measuring unit for determining a parameter directly related to dielectric polarization and an analysis unit for performing the analysis based on the determined parameter.
As described above for the inventive method, the parameter can be a voltage component, and the measuring unit can then contain two conductive surfaces (e.g. capacitor plates), a voltage source and a voltmeter.
In accordance with the above, the measuring unit can also contain a short-circuiting circuit (to create the potential difference.)
In this embodiment, the voltage source can generate alternating currents across the entire frequency spectrum (including direct current). With this embodiment, a low-frequency method, i.e. more suitable for frequencies under e.g. 10 Hz, is mainly used. One particularly suitable frequency that yielded good results in experiments is around 1 Hz.
In an alternative version of the measuring unit for determining another parameter related to dielectric polarization, the measuring unit has two capacitor plates, an inductive load connected to an oscillatory circuit formed with the capacitor plates, a alternating current source, a voltmeter and a timer.
An applied voltage pulse, or train of voltage pulses, in the oscillatory circuit will decay, and the decay time is a measure of dielectric polarization. So activating the oscillatory circuit is sufficient for performing the determination. However, the design with an oscillatory circuit makes it possible to use higher frequencies advantageously. A high-frequency pulse is then applied to the oscillatory circuit. The pulse can advantageously exceed 30-40 MHZ.
Wireless communications for excitation and detection can be performed with EM waves when high-frequency waves are used.
The decay can be established from part of the actual decay curve that can be obtained.
Since the first embodiment can advantageously be used for lower frequencies and the second embodiment for higher frequencies, the embodiments can be combined in a single measuring unit for measurement over a broad frequency spectrum. It should be noted, however, that each of the two embodiments could be used over a wide frequency range.